Secondary usage of a frequency is discussed as a measure for alleviating future depletion of frequency resources. The secondary usage of a frequency means that part of or all the frequency channels preferentially allocated for a system is secondarily used by the other system. Typically, a system which is preferentially allocated with a frequency channel is called a primary system and a system which secondarily uses the frequency channel is called a secondary system.
A TV white space is an exemplary frequency channel whose secondary usage is discussed (see Non-Patent Literature 1). The TV white space is a channel which is not used by a TV broadcast system depending on an area among frequency channels allocated for the TV broadcast system as a primary system. The TV white space is opened to a secondary system so that efficient utilization of the frequency resource is to be achieved. A standard for a physical layer (PHY) and a MAC layer for enabling the secondary usage of the TV white space can include IEEE802.22, IEEE802.11af and ECMA (European Computer Manufacturer Association)-392 (CogNea, see Non-Patent Literature 2 described later).
In the secondary usage of a frequency band, in general, the secondary system is required to be operated so as not to give a detrimental interference to the primary system. In order to do so, one of the important technologies is transmission power control. For example, Patent Literatures 1 described later proposes an approach to determine the maximum transmission power of a secondary system in response to a path loss of a path between the base station of the secondary system and the receiver device of the primary system.